﻿package {
	import flash.display.Sprite;
	public class Double extends Sprite{
		public var _product:Number;   //屬性
		
		public function Double(){
			init();
			}
		public function init() {
			   _product = 2;
		}
		public function exchange(num:Number):void{
				trace(num*_product);
				}
	}
}